Process and composition for coloring copper and copper alloy surfaces



Patented Feb. 8, 1949 H'EED PROCESS AND COMPOSITION FOR COLOR- INGCOPPER AND COPPER ALLOY SUB- FACES Walter E. Meyer, Hamden, Conn.,.assignor, by

mesne assignments, to- Enthone, Inc.,

New

Haven, Conn., a corporation of Connecticut No Drawing. ApplicationNovember 4, 1944, Serial No. 562,053

'1 Claims. (01. 148-614) This invention relates to the coloring ofcopper and copper alloy surfaces.

It is frequently desirable in the finishing of articles such as metalbuttons and buckles, costume and cosmetic accessories, lamp bases andstands, urns, screens, tacks, particularly upholstery tacks, buildershardware and architectural items, and the like, fabricated from copperand copper alloys, such as brass, to treat the surfaces of the articleto impart thereto a color not characteristic of the untreated metal.Various shades of brown including tan, greenish-brown, brownish-gold,etc., are considered particularly desirable. I

In accordance with the present invention, .I, produce these and othercolors on copper and copper alloy surfaces by a process which comprisescontacting the surface with an aqueous solution containing an alkali oralkaline earth metal chlorite, e. g. sodium, potassium, and calciumchlorites, and an alkaline salt. The alkali and alkaline earth metalchlorites are salts of chlorous acid and when chemically pure areessentially neutral in reaction. In the preferred mode of executing theprocess the surface to be cc]- ored is immersed in the salt solution.

Among the many alkaline salts which may be employed in the process of myinvention may be mentioned: sodium carbonate, sodium metasilicate,sodium tetraborate, trisodium phosphate, tetrasodium pyrophosphate,sodium sesquisilicate, sodium orthosilicate, and the correspondingpotassium and alkaline earth compounds where they are water-soluble. Ifdesired, the process may be executed using a plurality of alkaline saltsand/r chlorites. The presence of substantial amounts of a strong alkalisuch as sodium or potassium hydroxide in the coloring solution iswithout harmful efiect, in fact maybe advantageous particularly where itis desired to accomplish the coloring as rapidly as possible or toimpart colors other than shades of brown, for example, a bluish,purplish, or greenish color.

It will be understood that the words color and coloring are used hereinandv in the appended claims in the strict sense and do not include blackor blackening. I

The exact color produced on the surface treated depends upon variousfactors including the composition of the surface, the particular saltsbeing employed, the concentration of the salts, the temperature at whichthe solution is maintained, and the contact or treating time. tionsnecessary to achieve a particular color can be readily determined bysimple experiments well 2 within the skill of those experienced in themetal coloring art.

I have found that in most cases the solution with proper adjustment ofother conditions may be effectively operated at any temperature between70 F. and its boiling point. However, I

" prefer to operate the solution at temperatures tains the chlorite andalkaline salt in a ratio The condiby weight within the range 1:1 to122.5. Using such ratios of chlorite and alkaline salts, I have beenable in many cases to obtain equivalent results from saturated solutionsand solutions containing as little as a total of 4'. grams per literof-the salts. The less concentrated solutions, however, must usually beoperated at a higher temperature in order to accomplish the coloring inthe same length of time. In operating at high concentrations, I havenoticed that no adverse effect results from the presence of substantialamounts of undissolved salts in the solution. In general, I prefer toemploy a solution in which the concentrations of the salts are withinthe following limits: chlorite- 10 g./l., alkaline salt-20 g./l. tochlorite g./l., alkaline saltg./l. I usually employ sodium chlorite inthe practice of the invention because of its solubility and because itis readily available commercially.

Some combinations of the salts used in the execution of the inventiongive various colors while other combinations appear capable of impartingonly a relatively few colors or of giving only a single color. I havefound that the solution as prepared with sodium chlorite and eithersodium carbonate or trisodium phosphate will give the greatest number ofcolors of the various chloritealkaline salt mixtures. When prepared withborax or sodium metasilicate in lieu of sodium carbonate or trisodiumphosphate, the solution is relatively limited in coloring range. A veryattractive brownish-gold color may be achieved, however, with a solutioncontaining about 66 grams per liter of borax and an equal amount ofsodium chlorite. This solution is best operated at the boiling point. Ifsodium metasilicate is used instead of borax, a greenish to brown colorresults depending upon the temperature of operation and the length ofthe treating period.

I prefer to carry out my process in a container formed of low carbonsteel. The container or tank should be welded, not soldered,

ecause the solution will quickly dissolve solder. Inameled ware andceramic vessels are not recommended for use with solutions which alsoconiin caustic because such solutions will gradually ttaclr the enamelor ceramic and frequently the Jlution may be poisoned by components ofthe camel.

In making up the solution, the tank is usually lied about three-quartersfull of water after hich the pre-inixed salts are added with stirnguntil they are completely dissolved. The mk is then filled to theoperatinglevel with iditional water.

I have found that unlike pure chlorlte a mixire of a chlorlte and analkaline salt containing cm 1 to 2.5 parts of the alkaline salt for eachtll". of chlorlte is not explosive upon percussion the presence oforganic matter and does not arkedly increase the infiammability ofordinary brics when permitted to remain in contact lerewith. Also, themixture or composition is as reactive with sulfur and when brought intontact with acid is less prone to give oif danger-' LS amounts ofchlorine dioxide. This last charteristic of my composition isparticularly derable from the standpoint of safety since many etalsurface treatments involve the use of acid iutions which are sometimesrather carelessly .ndled. Thus, when'accidentally spilled about platingroom in which acid solutions are being ed, my composition does notinvolve the risk of lorine dioxide liberation that would be involved thechloritehandled separately were so spilled. consider the compositionresulting from intiitely mixing an alkali or alkaline earth metal loritewith an alkaline salt a part ofmy inven- ,n. Where it is desired topractice the process ing a highly alkaline solution, the composition tyinclude substantial amounts, i.e. up to 50%, sodium or potassiumhydroxide.

in commercial practice the composition conning 2 parts alkaline salt perpart chlorlte is ded to water to form the coloring solution in aproportion of about 1 lb. for each gallon of ter.

During the coloring operation, water should-be led from time to time toreplace that lost by lporation; otherwise, the solution may become lconcentrated. No precise analytical control the solution is required.The need for more 50 ts is indicated by a slowing up of the coloring e.When the coloring rate has dropped about t, I usually add about 4 ouncesof the original zture for each gallon of water present in the considerit highly important to thoroughly m the copper. or copper alloy surface.Cleancan he done with alkaline cleaners, vapor or or-solventde-greasers, or by emulsion clean- The cleaning is not as critical asthat for ting, but it is recommended to the end of ining uniformcoloring that the surface be med to the extent that water when placed onsurface remains thereon as a continuous film at least one minute withoutseparating into plets i. e.. no water-break. n the case of highly buifedsurfaces, it is ecially desirable to clean the surface to nolter-break." However, the work is preferably roughly rinsed aftercleaning and then dipped :odiu'm cyanide solution as in the instance ofitroplated copper.

have found that I can usually produce'the [red color on pure copper andhigh copper iys in from 1 to 10 minutes. In some cases 4 less than 30seconds is suilicient. Low copper alloys may require as long as 20minutes. After coloring, the work should be thoroughly rinsed in runningcold water and then in hot water if it 5 is to be dried.

I In the immersion treatment, small parts can be supported in steelbaskets or cylinders, and large objects on steel or iron racks, hooks,or wires. Where baskets are used, it is advisable to shake the workoccasionally so that all surfaces will be exposed to the solution.

Following the coloring operation, the work may be subjected to variousafter-treatments such as tumbling in saw-dust, corn cob drying meal, or

paraffin coated ground cork." Where the work must withstand severeoutdoor weathering, it is advisable to augment the protective effect ofthe finish with either lacquer, oil, or wax.

The herein described process is suitable for coloring all copper alloyscontaining as little as 60% of copper. Thus 60:40, 65:35, 70:30, 80:20,and 90:10 brasses are readily colored, as well as tin bronzes, siliconbronzes, beryllium coppers, and phosphor bronzes. Pure copper whethercast,

rolled, or electro-plated, is quickly given a deep finish. The processis also applicable to the coloring of electrolytically deposited brassalloys where the nominal copper content or the alloy is 60% or more.

I claim:

1. A solid composition in finely divided form adapted for use in aqueoussolution to color copper surfaces or surfaces of copper alloys containing not less than 60% copper which consists of about 1 part byweight of an alkali metal chlorlte and from about 1 to about 2.5 partsby weight of an alkaline salt having an alkalinity equal to or greaterthan that of tetrasodium pyrophosphate but less than that of causticsoda 40 or potash.

. 2. A solid composition in finely divided form' adapted for use inaqueous solution to color copper surfaces or surfaces of copper alloyscomprising not less than 60% copper which consists of about 1 part byweight of sodium chlorlte and about 2 parts by weight of an alkalinesalt having an alkalinity equal to or greater than that oftetrasodiumpyrophosphate but less than that of caustic sodayor potash.

.3. A process for coloring copper surfaces and surfaces of copper alloyscontaining not less than 60% copper which comprises contacting thesurface with an aqueous solution consisting essentially of water. achlorlte of the group consisting of alkali and alkaline earth metalchlo-.

rites, an alkaline salt having an alkalinity equal to,"or greater than,that of tetrasodium pyrophosphate but less than that of caustic soda orcaustic potash, in proportions by weight within the range of 1 to 2.5parts of the alkaline salt per part of the chlorlte, and 0 to 50%, basedon the total weight of the chlorlte and alkaline salt, of a causticalkali, the concentration of the salts in the solution being within therange of 4 grams per liter to saturation.

4. A process for coloring copper surfaces and A surfaces of copperalloys containing not less than V 60% copper whichcomprises immersingthe surface in a hot aqueous solution consisting essentially of water,an alkali metal salt of chlorous acid, an alkaline salt having'analkalinity equal to, or greater than, that of tetrasodium pyrophosphatebut less, than that of caustic soda or caustic potash, in proportions byweight within the range of 1 to 2.5 parts of the alkaline salt per partof the chlorite, the concentration of the salts in the solution beingwithin the range of 4 grams per liter to saturation.

5. A process for coloring copper surfaces and surfaces of copper alloyscontaining not less than 60% copper which comprises immersing thesurface in a hot aqueous solution consisting essentially of water,sodium chlorite and an alkaline salt having an alkalinity equal to, orgreater than, that of tetrasodium pyrophosphate but less than that ofcaustic soda or caustic potash, in proportions by weight of about 1 to2, the concentration of the chlorlte in the solution being within therange of 10 grams per liter to 80 grams per liter.

6. A solid composition in finely divided form adapted for use in aqueoussolutions to color copper surfaces and surfaces of copper alloyscontaining not less than 60% copper, the composition consistingessentially of a chlorite of the group consisting of the alkali andalkaline earth metal chlorites, an alkaline salt having an alkalinityequal to, or greater than, that of tetrasodium pyrophosphate, but lessthan that 01 caustic soda or caustic potash, in proportions by weightwithin the range of 1 to 2.5 parts of the alkaline salt per part of thechlorite, and 0 to 50% based on the total weight 01' the chlorite andalkaline salt of a caustic alkali.

7. A solid composition in finely divided form for use in aqueoussolution to color copper surfaces or surfaces of copper alloyscontaining not less than 60% copper, the composition consistingessentially of an alkali metal chlorite, an alkaline salt having analkalinity equal to, or greater than, that of tetrasodlum pyrophosphatebut less than that of caustic soda or caustic potash, in proportions byweight within the range of 1 to 2.5 parts of the alkaline salt per partof the chlorite, and 0 to 50% based on the total weight of the chloriteand alkaline salt of a caustic alkali.

WALTER R. MEYER.

REFERENCES CITED The following references'are of record in the file ofthis patent:

UNITED STATES PATENTS Meyer Dec. 12, 1944

